\begin{tikzpicture}[scale=3, 
    help lines/.style={very thin, color=#1!50},
    help lines/.default=blue,
    information text/.style = {rounded corners, fill = red!10, inner sep=1ex}
    ]
    % Colors
   \colorlet{anglecolor}{green!50!black}
   \colorlet{sincolor}{red}
   \colorlet{tancolor}{orange!80!black}
   \colorlet{coscolor}{blue}
    \draw[->, semithick] (0, -1.5) -- (0, 1.5);
    \draw[->, semithick] (-1.5, 0) -- (1.5, 0);
    \draw (0, 0) circle (1);
    \draw [step=0.5cm, help lines=gray] (-1.4, -1.4) grid (1.4, 1.4);
    \shadedraw[left color=gray, right color=green, draw=green!50!black]  (0mm,0mm) -- (3mm, 0mm) arc [start angle=0, end angle=30, radius=3mm] -- cycle;
    \draw(15:2mm)node[color=anglecolor]{$\alpha$};
    \draw[very thick, color=sincolor] (30:1cm) -- node[left]{$\sin\alpha$} +(0, -0.5cm);
    \draw[very thick, color=coscolor](30:1cm)++(0, -0.5cm) -- node[above]{$\cos\alpha$} (0,0);
    \path[name path=sloped line] (0,0) -- (30:1.5cm);
    \path[name path=upward line] (1cm, 0) -- (1cm, 1.5cm);
    \draw [name intersections={of=sloped line and upward line, by=t}](0,0) -- (t);
    \draw [very thick, color=tancolor] (1, 0) -- node[right]{$\tan\alpha$}(t);
    \foreach \x/\xtext in {-1, -0.5/-\frac{1}{2}, 0.5/\frac{1}{2}, 1}
        {
            \draw[thick] (\x cm, 0) -- node[anchor=north, fill=white]{$\xtext$}(\x cm, -1pt);
            \draw[thick] (0, \x cm) -- node[anchor=east, fill=white]{$\xtext$}(-1pt, \x cm);
            
        }
    \draw[xshift=1.8cm, yshift=0cm] (0,0) node[right, text width=6cm, information text]{
        The {\color{anglecolor} angle $\alpha$} is $30^\circ$ in the
        example ($\pi/6$ in radians). The {\color{sincolor}sine of
        $\alpha$}, which is the height of the red line, is
        \[
        {\color{sincolor} \sin \alpha} = 1/2.
        \]
        By the Theorem of Pythagoras ...
       };    

\end{tikzpicture}
 